Work vehicles including, but not limited to, agricultural work vehicles, such as tractors and combines, as well as construction vehicles, such as loaders and backhoes, are often supported by a set of inflatable tires. The inflation pressure of these inflatable tires can be adjusted to provide a substantially cushioned ride while providing adequate traction and support for the vehicle. Maintaining proper tire inflation provides better maneuverability and control of the work vehicle while minimizing the amount of vehicle slip, thereby increasing the amount of traction and power available for the vehicle. Further, maintaining proper tire inflation reduces the amount of fuel necessary during operation of the work vehicle and provides improved tire wear, thereby providing substantial fuel cost savings.
A number of factors and conditions exist which cause work vehicles to be operated despite having a non-optimal or improper tire inflation pressure. For example, tire inflation pressure is typically decreased gradually over time to a low-level by leaks and imperfect seals, and typically tire inflation pressure fluctuates as a function of temperature. In addition, the optimal tire inflation pressure will vary based upon the operating conditions of the work vehicle, such as the vehicle speed, the type of terrain, and the mission. In addition, the optimal tire inflation pressure will depend upon the operating loads placed on the tires under various operating conditions.
One characteristic that is especially susceptible to changes in vehicle speed, terrain, and mission, is slip of the vehicle tires. Tire slip may be controlled by changing the contact area the tire has with the operating surface, which may be soil, rocks, asphalt, concrete or other surfaces over which a work vehicle may be traversing. Therefore, slip may be controlled by changing the tire contact area with the ground. One such method of controlling the tire contact area is by changing tire inflation pressure.
A traditional method of changing tire inflation pressures to match the operating surface conditions is to manually measure the inflation pressure of each tire and then, for each tire, to manually add air to increase pressure or to manually deplete air to decrease pressure, and thereby to change the tire contact area. The effectiveness of the traditional method depends in part on the diligence of the operator in adjusting the tire inflation pressures, therefore the manual method can be cumbersome due to the numerous tires found on many work vehicles. To address the drawback of the traditional method, central tire inflation systems, operable from the operator's compartment or cab of the work vehicle, have been developed for military vehicles, commercial trucks, and agricultural vehicles.
Existing central tire inflation systems require that the vehicle operator view information regarding the tire inflation pressure and manually adjust the tire inflation pressures using input devices. During operation, such existing central tire inflation systems may also maintain the predetermined tire inflation pressures set by the operator. Such existing central tire inflation systems, however, do not account for dynamic variations in the tire slip caused by changes in terrain, by changes in the weight of materials stored on the vehicle, and by weight transfers associated with implements attached to the work vehicles. The weight of materials stored on a harvesting vehicle, for example, will vary dramatically as harvested crop is alternately loaded into and unloaded from one or more crop storage bins supported by the vehicle during harvesting operations. The attached implements may include, for example, a mounted implement such as a plow mounted to a hitch assembly supported by an agricultural tractor, or a drawn implement such as a planter or other material spreader (e.g., a fertilizer or insecticide spreader) attached to a draw bar pulled by such a tractor. Such mounted or drawn implements exert varying loads on the tractor depending on, for example, the depth of the plow as it is being pulled through a field, or the amount of material remaining in the planter or spreader, or the condition of the surface including characteristics such as the soil type, soil moisture content, soil compaction, etc. These varying loads cause variations in the tire slip associated with the work vehicle.
Thus, there is a need and a desire for a central tire inflation system that provides for vehicle slip control automatically during vehicle use. Also, there is a need and desire for a central tire inflation system for a work vehicle that provides proper tire inflation pressures over varying combinations of load, speed, terrain, and mission, and optimizes the amount of slip seen by the vehicle tires. There is also a need and a desire for a central tire inflation system for a work vehicle supported by inflatable tires, wherein the central tire inflation system can account for changes in tire slip due to varying loads placed on the work vehicle by attached implements, or by material loaded into or unloaded from one or more storage bins supported by the work vehicle during operations of the work vehicle.